1. Field
The present disclosure herein relates to a phase interpolation circuit, and more particularly, to a phase interpolation circuit exactly and stably performing a phase interpolation operation even in a wide range frequency input, and an output characteristics stabilizing method thereof.
2. Description of the Related Art
A phase interpolation circuit that performs a phase interpolation operation in a clock data recovery circuit has been known in the related art.
A buffer having a fixed output resistance value is widely used in a phase interpolation circuit including a phase interpolator. Since such an interpolator is designed to show optimal performance with respect to only a preset frequency input, the pattern of phase interpolation output may be changed according to the shape of an input waveform in a wide range frequency input that falls outside the range of the present frequency input. Particularly, if an input waveform of a phase interpolator becomes a rectangular wave in a lower frequency, a phase interpolation output may be set to an erroneous value.
In order for a phase interpolator to generate a constant phase interpolation output of a phase step, the input waveform has to become closer to a triangular wave. If the input waveform becomes a rectangular wave, i.e., a differential input has a section having a DC value simultaneously, the phase interpolation output may have an uncertain value.
If a buffer having a fixed output resistance value is used in a wide range frequency input, it is difficult to provide the input waveform of the phase interpolator as a triangular wave at both a low frequency and a high frequency. Thus, a phase interpolation operation of the phase interpolator may not be accurately and stably performed. Accordingly, an improved technique capable of accurately and stably performing a phase interpolation operation is necessarily required over a wide range frequency input.